During manufacture of display screens, the display screens are inspected for various flaws. Those which fail quality control testing are often relegated to a trash heap or saved for applications, which have lower quality requirements. Consumer grade electronics generally require high quality displays to pass all quality control inspections, which leads to reduced yields and increased costs due to minor flaws.
One common flaw type is a non-functioning pixel, which includes bright pixels (e.g., hot pixels) and dark pixels (e.g., dead pixels). In a liquid crystal display (“LCD”), bright pixels are pixels with a defect that causes the liquid crystal material to always transmit light through the pixel. Dark pixels are pixels with a defect that causes the liquid crystal material to always block light from passing through the pixel.
The ISO-13406-2 Standard specifies defect classes, which define the number and type of defective pixels permissible in each class type. For example, many display manufactures specify their displays as pixel fault class II, which means two or less hot or dead pixels per million pixels. These strict fault standards reduce display yields at each pixel fault class. Methods exist for trying to fix non-functioning pixels, such as targeting individual pixels for additional processing (for example, laser etching away electrical shorts), but can introduce substantial additional costs into the manufacturing flow.